Electrolytic four-channel device and method

ABSTRACT

An electrolytic device includes four channels separated by three charged barriers. The device can be used to suppress an eluent stream containing separated sample analyte ions and/or to pretreat a sample stream containing unseparated analyte ions.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation and claims the prioritybenefit of co-pending U.S. patent application Ser. No. 14/028,064 filedSep. 16, 2013, which application is hereby incorporated herein byreference in their entireties.

BACKGROUND OF THE INVENTION

The present invention relates to an electrolytic device suitable for usein a liquid chromatographic system.

Suppressed ion chromatography is a known technique for analysis ofsample ions of one charge in an eluent containing electrolyte. First,the sample ions in the eluent are chromatographically separated. Then,the eluent is suppressed by removal of the electrolyte counterions tothe sample ions, and the sample ions are detected, typically by anelectrical conductivity detector. One type of suppressor device, calleda sandwich membrane suppressor, is described in U.S. Pat. No. 4,999,098(the “'098 patent”). In one embodiment, the suppressor includes threechannels. During suppression, the eluent and separated sample ions flowthrough the central channel of the suppressor while regenerant solutionflows in the two outside channels. The outside two channels areseparated from the central channel by barriers having exchangeable ionscapable of passing ions of only one charge, positive or negative, and ofblocking bulk liquid flow. Suitable barriers are ion-exchange membranessold under the trademark Nafion®. One embodiment is an electrolytic,three-channel flat membrane suppressor illustrated in FIGS. 2 and 3 ofthe '098 patent. For an anion analysis, the eluent including the analyteanions which have been previously separated on a chromatographic column,comprising a packed bed of anion exchange resin, flows through thecentral channel. The ion-exchange membranes include exchangeablecations. Eluent cations are removed from the central channel and aredrawn toward the negative electrode across the adjacent membranebarrier, as illustrated in FIG. 3 of the '098 patent. Thus, if sodiumhydroxide is used as the electrolyte of the eluent, the sodium ion isremoved from the central channel across the cation exchange membraneadjacent to the cathode. A three-channel device of this type has alsobeen used for purposes other than suppression such as pretreatment of aliquid sample prior to chromatographic separation.

SUMMARY OF THE INVENTION

One embodiment of the invention is an electrolytic device suitable foruse in a liquid chromatography system. The device comprises a housingincluding at least first, second, third, and fourth side-by-side liquidflow-through channels, each having an inlet and an outlet; said firstchannel being separated from said second channel by a first chargedbarrier having exchangeable ions capable of passing ions of only onecharge, positive or negative, and of blocking bulk liquid flow; saidsecond channel being separated from said third channel by a secondcharged barrier having exchangeable ions capable of passing ions of thesame charge, positive or negative, and of blocking bulk liquid flow;said third channel being separated from said fourth channel by a thirdcharged barrier having exchangeable ions capable of passing ions of thesame charge, positive or negative, and of blocking bulk liquid flow; afirst electrode disposed adjacent to and along said first channel inelectrical communication therewith; and a second electrode disposedadjacent to and along said fourth channel in electrical communicationtherewith.

Another embodiment is a method for pretreating a liquid sample streamcontaining unseparated analytes of one charge, positive or negative, andcounterions to said analyte ions and for suppressing eluent containingpreviously separated sample analytes of one charge, positive ornegative, in the above electrolytic device. The method comprises flowingsaid eluent containing said separated analytes into said second channelinlet through said second channel and out said second channel outlet;flowing said liquid sample containing unseparated analytes into saidthird channel inlet through said third channel and out said thirdchannel outlet; and applying an electric current between said first andsecond electrodes of opposite charge across said first, second, thirdand fourth channels to cause ions of opposite charge to said separatedsample analytes in said liquid sample and eluent to flow toward the oneof said two electrodes of the opposite charge to first charged barrierexchangeable ions to remove at least some of said counterions in saidliquid sample stream exiting said third channel outlet andsimultaneously suppressing said eluent flowing out of said secondchannel outlet.

Another embodiment is a method for suppressing eluent containingpreviously separated sample analytes of one charge, positive ornegative, in the above electrolytic device to convert the separatedanalytes to acid or base form and for converting said acid or base formseparated analytes in the suppressed eluent to salt form. The methodcomprises flowing said eluent containing said separated analytes intosaid second channel inlet through said second channel and out saidsecond channel outlet; and flowing said eluent from said second channeloutlet to said third channel inlet and through said third channel tosaid third channel outlet and thereafter to a second detector; said flowthrough said second and third channels being countercurrent.

A further embodiment is another method for treating a sample stream inthe above electrolytic device. The method comprises flowing said samplestream into said second channel inlet through said second channel andout said second channel outlet; and flowing aqueous streams through saidfirst, third and fourth channels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a four-channel electrolytic deviceaccording to the present invention.

FIG. 2 is a schematic view of the device of FIG. 1 illustrating ionicflow when the device is used for a combination of sample pretreatmentand suppression.

FIG. 3 is a schematic view of a system using the device of FIG. 2 withvalving set in a position to pretreat the liquid sample in the deviceand to load the sample into a sample retainer.

FIG. 4 is a schematic view of the apparatus of FIG. 3 with valving setfor injection of the liquid sample in the sample retainer into achromatography column.

FIG. 5 is a schematic view of a four-channel device for pretreatment ofa sample stream containing unseparated analytes and suppression of theeluent illustrating ionic flow.

FIG. 6 is a schematic view of a system using the device of FIG. 5 withthe valving set to load the sample into a sample retainer.

FIG. 7 illustrates the system of FIG. 6 with the valving set to injectthe liquid sample in the sample retainer into a chromatography column.

FIG. 8 is a schematic view illustrating ionic flow of the four-channeldevice used for suppression and conversion of previously separatedanalyte ions to salt form.

FIG. 9 is a schematic view of a system using the device of FIG. 8, withthe valving set to load the unseparated sample into a sample retainer.

FIG. 10 illustrates the system of FIG. 9, with the valving set to injectthe liquid sample in the sample retainer into a chromatographic column.

FIG. 11 is a schematic expanded view of the four-channel device used fordouble-pass suppression illustrating ionic flow.

FIG. 12 is a schematic view of a system using the device of FIG. 11,with the valving set to load the sample liquid containing unseparatedsample analytes in a sample retainer.

FIG. 13 is a schematic view of a system using the device of FIG. 12,with the valving set to inject the liquid sample in the sample retainerinto a chromatography column.

FIG. 14 is a schematic view of ion flow for using the four-channeldevice for suppressing a solvent-containing eluent.

FIG. 15 is a chromatogram illustrating anion analysis using samplepretreatment and suppression in accordance with FIGS. 1 and 2.

FIG. 16 is a chromatogram illustrating anion analysis using suppressionwithout sample pretreatment.

FIG. 17 is a chromatogram illustrating anion analysis using suppressionwith a single pass through a channel.

FIG. 18 is a chromatogram illustrating anion analysis using double passsuppression in accordance with FIGS. 11-13.

FIG. 19 is a chromatogram illustrating cation analysis using suppressionwithout sample pretreatment.

FIG. 20 is a chromatogram illustrating cation analysis using samplepretreatment and suppression in accordance with FIG. 1.

FIG. 21 shows thirty superimposed chromatograms illustrating excellentreproducibility of the cation separations using an apparatus inaccordance with FIG. 1.

FIG. 22 is a chromatogram illustrating anion analysis using aconcentration step and suppression without sample pretreatment.

FIG. 23 is a chromatogram illustrating anion analysis using aconcentration step and suppression with sample pretreatment inaccordance with FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In general, the present invention relates to an electrolytic deviceincluding at least four channels and use of the device in analysis of aliquid samples containing analyte ionic species of one charge, positiveor negative, e.g., for use in liquid chromatography, specificallysuppressed ion chromatography.

The use of an electrolytic three-channel device for suppression in ionchromatography is illustrated in the '098 patent, the disclosure ofwhich is incorporated by reference herein. A major difference of thepresent device from a three-channel device is the use of one or moreadditional channels. The device includes at least three charged barriersinstead of the two barriers of the '098 patent, but otherwise may be ofthe same structure.

FIG. 1 illustrates a schematic view of a four-channel device 8. Thedevice includes a housing, not shown, such as of the type illustrated inFIG. 2 of the '098 patent but with suitable ports for the fluidic inletsand outlets. Device 8 defines first, second, third, and fourthside-by-side liquid flow channels, each having an inlet and an outlet. Afirst channel 10, including ports 10 a and 10 b, is defined bysurrounding gasket 10 c; a second channel, 12, including ports 12 a and12 b, is defined by gasket 12 c; a third channel, 14, including ports 14a and 14 b is defined by gasket 14 c; and a fourth channel, 16,including ports 16 a and 16 b, is defined by gasket 16 c. The channelsare side-by-side liquid flow-through channels. Channel 10 is separatedfrom channel 12 by a charged barrier 18, having exchangeable ionscapable of passing ions of only one charge, positive or negative, and ofblocking bulk liquid flow. Channel 12 is separated from channel 14 by acharged barrier 20 of the same type as barrier 18. Channel 14 isseparated from channel 16 by charged barrier 22, also of the same typeas barrier 18.

It should be noted that the channels 10, 12, 14 and 16 can be defined bysolid materials such as PEEK and have an elastomeric seal materialadjacent to the barriers in place of the gasket material to make a sealon the perimeter of the channels 10, 12, 14 and 16. Hardware of thistype is described in application entitled “Suppressor Device”.(application Ser. No. 13/674,738, filed Nov. 12, 2012.)

A first electrode 24 is disposed adjacent to channel 10. A secondelectrode 26 is disposed adjacent to channel 16. Electrodes 24 and 26may be in direct contact with the liquid flowing through channels 10 and16, respectively, or may be separated from such liquids so long as theelectrodes are in electrical communication with the liquid flowingthrough channels 10 and 16, respectively. For example, the electrodes 24and 26 can be in direct contact with membrane 18 and 22. Electrodes 24and 26 are connected to a conventional power source, not shown, so that,when the power is turned on, an electric field is applied between theelectrodes across the liquid flowing through all four channels. At theanode, water is electrolyzed to hydronium ion and oxygen gas and at thecathode water is electrolyzed to hydroxide ion and hydrogen gas.

Flow-through structure such as neutral screens, or charged screens ofthe same charge as the exchangeable ions of the barriers not shown, maybe disposed in one or more of the channels as illustrated in the '098patent. Also, a bed of neutral particles or ion exchange particles maybe disposed in the channels. In that regard, the structure of theelectrolytic four-channel device, including the charged barrierseparating the channels and the overall structure of the device, may bethe same as that of the '098 patent, except for the additional barrierand the additional channel which may serve one of many functions such asset forth in the many applications for the device described hereinafter.

FIGS. 2-4 illustrate a four-channel device used for a combination ofsample pretreatment and suppression. Like parts will be used todesignate like numbers for the four-channel device of FIG. 1.

Referring to FIG. 3, the sample pretreatment and suppression system isused with valving set in a first position for loading of the sample intoa concentrator or sample loop, referred to collectively herein as “asample retainer”. As illustrated, a pump 30 pumps eluent from anoptional eluent generator 32 through line 34 to valving 36 in the formof a six-way valve set for loading of the sample into the sampleretainer 58. Alternatively, other types of single or multiple valvesmust also be used. Valving 36 includes six ports, 36 a-f As illustrated,ports 36 b and 36 c are open so that eluent in line 34 flows in line 38to a chromatographic separator 40 such as chromatography column,including an inlet 40 a and an outlet 40 b, of a conventional type,e.g., including a packed bed of ion exchange packing, and from there inline 42 to port 12 a of channel 12 of the four-channel device 8.Separator outlet 40 b is upstream of and in fluid communication withchannel inlet 12 a and outlet 12 b is upstream of and in fluidcommunication with detector 46. In the sample loading setting of valving36, the liquid stream flowing through channel 12 may include no sample.The liquid stream exiting outlet 12 b flows in line 44 to a detector 46,illustrated as a conductivity cell, and from there in line 48 to inletport 10 a of channel 10 and out outlet port 10 b to line 50 to recycleinto inlet port 16 a of channel 16 and out outlet port 16 b to waste.This stream may be used as a source of water for other electrolyticdevices and to carry waste streams carrying ions and gases.

Referring again to FIG. 3, in this first positioning of valving 36 forsample loading, a liquid sample stream flows to inlet port 14 a ofchannel 14 and out outlet port 14 b in line 54 to ports 36 e and 36 d toa sample retainer 58 in the form of a concentrator column or sample loopof a conventional type. If sample retainer 58 is a concentrator column,the sample ions of one charge, positive or negative, are retained inretainer 58, typically a packed ion-exchange resin bed with exchangeableions of the same charge as the sample ions, and the remaining eluentflows in line 60 through ports 36 a and 36 f to waste. If sampleretainer 58 is a sample loop, a measured amount of sample is retained ina sample loop. In this position of valving 36, sample is loaded insample retainer 58 for a sample injection into the system as illustratedin FIG. 4 with valving 36 set in the second position.

A conventional eluent is provided, such as a cation hydroxide, e.g.,sodium hydroxide or potassium hydroxide for anion analysis. The eluentgenerator 32 may be of a conventional type, such as illustrated in U.S.Pat. No. 6,955,922. Alternatively, eluent may be provided from a source,not shown, such as an eluent reservoir.

Referring to FIG. 4, in a second position of valving 36, set for sampleinjection into column 40, eluent from eluent generator 32 is pumped bypump 30 in line 34 through ports 36 b and 36 a through line 60 to carrysample in sample retainer 58 in line 56 through ports 36 d and 36 c toline 38 to inlet port 40 a of chromatographic separator 40 and outoutlet port 40 b through line 42 into channel 12 and from there throughdetector 46, channel 10 and channel 16 to waste. Sample containing ions,positive or negative, are separated in column 40. Suppression takesplace in channel 12, as will be described. The suppressed liquid sampleflows in the eluent stream through detector 46, in which the separatedsample analyte ions are detected. As is conventional, a suppressorsuppresses the conductivity of the electrolyte ions of the eluent ofeffluent from column 40 which are of opposite charge to the ions beingdetected. Thus, for sample anion analysis, the suppressed eluentelectrolyte ion is of opposite charge to the sample anions, i.e., acation. Thus, for anion analysis, the electrolyte can be sodiumhydroxide or potassium hydroxide or a salt such as sodium or potassiumcarbonate and/or bicarbonate.

When detector 46 is a conductivity cell, the presence of ionic speciesproduces an electrical signal proportional to the amount of ionicmaterial. Such signal is typically directed from the conductivity cellto a conductivity meter permitting detection of the concentration ofseparated ionic species.

Referring to FIG. 2, ionic flow of a four-channel device, according tothe invention, is illustrated for a sample pretreatment and suppressionin the system illustrated in FIGS. 3 and 4. FIG. 2 illustrates anionanalysis, showing chloride as one of the anions to be separated andsodium hydroxide as the electrolyte of the eluent. Flow through channel12 is in the sample inject mode of FIG. 3. Eluent, including sodiumhydroxide, carries the separated analytes represented by the chlorideanion through channel 12. For anion analysis, electrode 24 is positivelycharged (an anode) and electrode 26 is negatively charged (a cathode).Charged barriers 18, 20, and 22, typically ion exchange membranes, e.g.Nafion®, include exchangeable ions of the same charge as the eluentcations to be suppressed. Note that Nafion is a sulfonatedtetrafluoroethylene based fluoropolymer-copolymer. Thus, barriers 18,20, and 22 include exchangeable cations, e.g., sodium for anionanalysis. When a potential is applied between electrodes 24 and 26, thesodium ions flow across barriers 20 and 22 toward cathode 26 to channel16 and out port 16 b to suppress the conductivity of the eluent whichflows out port 12 b. As illustrated, the pretreated analyte anions(chloride) are shown in acid form exiting port 12 b. The functionperformed in channel 12 is the same as the suppression functionperformed in the central channel of a conventional electrolytic samplesandwich suppressor such as illustrated in the '098 patent. In channel14, the sample in the sample stream is pretreated prior to loading ofsample retainer 58. A continuous flow of liquid is maintained in allchannels, during the loading of sample into sample retainer 58 in FIG. 3and during sample injection into chromatographic column 40, in theinjection position of FIG. 4.

Referring again to FIG. 2, as set forth above, sodium and calcium ionsare illustrated as the counter-ions in the sample of opposite charge tothe anion analytes to be separated and detected. The sodium and calciumions flow across barrier 22 into channel 16 for removal from the liquidsample prior to sample loading on sample retainer 58. Thus, the sampleexiting outlet port 14 b, which flows to sample retainer 58, is inacidic form.

In the past, sample pretreatment has been performed using asuppressor-like device, similar to that of the '098 patent. However,there are significant advantages in performing sample pretreatment andsuppression in a single device as illustrated in FIGS. 2-4. For example,it lowers the overall cost because a single power supply can be used toperform both functions. Also, if the sample is of a type which tends toprecipitate when injected into the system, such precipitated samples canget lodged into a chromatographic column. Thus, due to the high pHcondition for anion analysis, multivalent cationic species, such ascalcium and magnesium, tend to precipitate. By removal of suchcounter-ions to the analyte ions to be analyzed, the columns are notsubject to precipitation. For example, in suppression, due to the acidicnature of the functional groups, the precipitation can be induced at arelatively higher concentration. Also, due to non-precipitating cations,the effective concentration of the precipitating ions is diminished. Ineffect, by removing the precipitating ions before analysis, theanalytical system is free from these ions and analysis proceeds withoutinterruption. This enables use without removal of such ions in aseparate device, e.g. an ion exchange cartridge, before analysis.

The following is a summary of the functions of the system for the twopositions of valving 36 as illustrated on FIGS. 3 and 4. In a firstposition, illustrated in FIG. 3, the liquid sample stream can be loadedinto sample retainer 58 and is blocked from flow to chromatographicseparator 40. In the second position, illustrated in FIG. 4, sample insample retainer 58 is in fluid communication with column 40 and iscarried to column 40 by eluent from eluent generator 32.

The suppression and sample pretreatment device of FIGS. 2-4 isillustrated for analysis of anions in a cation hydroxide or a salteluent in which the eluent cations are suppressed. The invention is alsoapplicable to the analysis of cations and suppression of electrolytecounter-ions (anions) in an eluent of opposite charge to the cationanalytes. In this instance, the polarity of all elements in the deviceis reversed. Thus, the barriers are positively charged, i.e., andinclude exchange ions of negative charge, and the polarities of theelectrodes are reversed during operation. Suitable eluents for anionanalysis include alkali hydroxides, such as sodium hydroxide orpotassium hydroxide, and alkali carbonates and bicarbonates. A suitableeluent solutions for cation analysis is methanesulfonic acid (MSA).

Channels 10 and 16 serve multiple functions similar to the outsidechannels of the prior art three-channel sandwich membrane deviceillustrated the '098 patent. One function is to provide the flowingstream to remove the eluent counter-ions to the analyte ions and thecounter-ions to the analyte ions in the sample ions in the pretreatmentchannel 14. Although a recycle configuration is shown in the figure, anexternal regenerant stream could be used for this function.

As illustrated in FIGS. 2-4, electrodes 24 and 36 are coextensive withand substantially parallel to barriers 18 and 22, respectively. Also, asillustrated in FIGS. 2-4, flow through suppressor channel 12 andpretreatment channel 14 is concurrent. The illustrated barriers aresubstantially flat or planar and the channels are substantially flat.However, concentric tubes could be used with one channel at the centerand the other channels formed in the external annular spaces asillustrated in FIGS. 7 and 8 of U.S. Pat. No. 6,077,434.

The four-channel device of FIG. 1 may be used in a variety of othersystems for analyzing analytes in a liquid sample. Thus, such systemsmay be used solely for pretreatment or solely for suppression in asuppressed ion chromatography system or both. Also, the invention alsoencompasses devices with five channels (or more) constructed like thefour channel device but with an additional charged barrier for eachadditional channel.

FIGS. 5-7 illustrate the four-channel device of FIG. 1, in a system inwhich the sample is converted to salt form prior to flow to sampleretainer 58, instead of acid form for anion analysis, as in FIGS. 2-4.The principal difference between the embodiments of FIGS. 2-4 and thatof FIGS. 5-7 is that, instead of concurrent flow as in the formerembodiment, flow through suppressor channel 12 is in countercurrent tothat of flow through sample pretreatment channel 14 in the latterembodiment. Like parts will be designated with like numbers for theembodiments of FIGS. 2-4 and FIGS. 5-7.

Ports described as inlets and outlets herein are ports which can servethe function of an inlet or an outlet. Thus, the same designations forthese ports will be used even if the flow may be reversed so that aninlet port may be an outlet port and vice versa for subsequentembodiments.

Referring to FIG. 6, valving 36 is set in the first position for sampleloading as in FIG. 3. Flow from pump 30 through column 40, channel 12,detector 46, channel 10 and channel 16 are the same as for FIG. 3. Theprincipal difference is that the sample flowing through channel 14 flowsfrom port 14 b to port 14 a, so that port 14 a is an outlet and port 14b is an inlet, whereas in FIG. 3, port 14 a is an inlet and port 14 b isan outlet. Thus, flow through channel 12 is countercurrent to flowthrough channel 14, as illustrated in FIG. 6. The stream flowing outport 14 b flows in line 54 to sample retainer 58, as illustrated in FIG.3.

Referring to FIG. 7, the system is the same for sample injection as forthe embodiment of FIG. 4 except that, as in FIG. 6, sample flow throughsample pretreatment channel 14 is countercurrent to flow throughsuppressor channel 12.

FIG. 5 is a schematic representation of ion flow in of the device ofFIGS. 6 and 7, illustrating a countercurrent flow in channels 12 and 14.As illustrated in FIG. 5, the sample flowing into port 14 b is convertedinto a salt as it exits port 14 a. As illustrated, the sample flowing inline 52 into port 14 b includes sodium and calcium counter-ions, whichare removed from channel 14 and flow across barrier 22 in the form of acation exchange membrane. However, near exit port 14 a, the eluententering channel 12 through inlet 12 a, adjacent to the exit end ofchannel 14, still includes a high concentration of cations becausesuppression is just beginning. Thus, for sodium hydroxide electrolyte inthe eluent, the sodium ions in the eluent flowing into port 12 a, areillustrated as flowing across cation exchange barrier 20 intopretreatment channel 14, and the analyte ions, illustrated as chloride,form sodium chloride salt which exits port 14 a for loading into sampleretainer 58. Thus, the sample anions exiting port 14 a are in the saltform of the electrolyte in the eluent.

An advantage of converting to the salt form by countercurrent flow inchannels 12 and 14 can be illustrated by analysis of cations. If flowwere concurrent as in FIGS. 2-4, the calcium hydroxide would be thepost-suppressor product, which tends to precipitate at highconcentrations. By using countercurrent flow as in FIGS. 5-7, the samplecan be injected into separator 40 as a salt, such as calcium methanesulfonate, which does not precipitate.

Referring to FIGS. 8-10, the device of FIG. 1 is used for saltconversion after suppression without sample pretreatment. Like parts bedesignated with like numbers as for FIGS. 2-8.

FIG. 9 illustrates valving 36 in a sample loading position in whichsample is loaded into sample retainer 58. Here the liquid sample is notpretreated in four-channel device 8. Instead, the liquid sample streamflows in line 70 through ports 36 e and 36 d to load sample retainer 58and from there through line 60, ports 36 a and 36 f to waste. Liquidstreams flow continuously through the system. Eluent is pumped throughline 34, ports 36 b and 36 c through column 40 and through inlet port 12a through channel 12, detector 46, and then through port 14 b channel14, outlet port 14 a, line 72, a second detector 74, line 76 to inletport 10 a through channel 10, outlet port 10 b, line 50, into inlet port16 a of channel 16 and outlet port 16 b to waste. Flow through channels12 and 14 is countercurrent.

FIG. 10 illustrates the system of FIG. 9 with valving 36 set to inject asample into column 40. The liquid sample stream in line 70 flows throughports 36 e and 36 f to waste. Eluent in line 34 flows from eluentgenerator 32 through ports 36 b and 36 a, line 60, to carry sample insample retainer 58 to ports 36 d and 36 c, line 38 to column 40, line 42to inlet port 12 a, channel 12, to outlet port 12 b detector 46, inletport 14 b, channel 14, outlet port 14 a through line 72 and past asecond detector 74 for detection. The outlet from detector 74 flowsthrough inlet port 10 a, channel 10, outlet port 10 b in line 50 intoport 16 a, channel 16 and out port 16 b to waste. Here again, flowthrough channel 12 is countercurrent to flow through channel 14.

In the system of FIG. 10, suppression is performed in channel 12 fordetection in detector 46 in a similar manner to that of a conventionalsandwich suppressor such as is set forth in the above '098 patent. Thus,the anion or cation analytes are in acid or base form, respectively.Flow from detector 46 is back through channel 14 in a countercurrentdirection and the sample analytes are converted to salt form fordetection in detector 74 as illustrated in the schematic diagram of ionflow of FIG. 8. Here, when the eluent is near the inlet of channel 12,suppression is in an early stage and so the eluent counter-ion to thesample ion is still highly concentrated. Such counter-ions, sodium asillustrated, flow across membrane 20. The solution exiting channel 12through port 12 b is detected by detector 46 and then is recycled backthrough inlet port 14 b to channel 14 and is converted to salt form bythe sodium ions flowing across membrane 20 near the inlet of channel 12to convert the eluent, containing separated sample ions, illustrated aschloride, in channel 14 to the salt form. Thus, as illustrated, chlorideis converted to sodium chloride form.

In this embodiment the suppressed and salt forms may be detected bydetectors 46 and 74, respectively. To illustrate the advantage of this,weak base such as ammonium ion response gives a non-linear fit withconcentration when performing suppressed chromatography, but bycombining with a salt converter, a linear fit can be achieved. Thus, theweakly dissociated species can be analyzed effectively along withstrongly dissociated species by the present invention.

Other embodiments of the invention are methods for treating a samplestream in the above electrolytic device in which the sample stream flowsinto the second channel inlet through the second channel and out thesecond channel outlet, and aqueous liquid streams flow through thefirst, third and fourth channels (“the aqueous liquid streamembodiments”).

FIGS. 11-13 illustrate one of the aqueous liquid stream embodiments, inwhich the apparatus of FIGS. 8-10 is used to provide a double pass (i.e.two passes) of the eluent and separated sample analytes through thefour-channel device 8 for suppression. Here, the aqueous liquid streamin the third channel is the stream flowing from the second channeloutlet to the third channel inlet. This embodiment is used forsuppression and includes no sample pretreatment. Like parts will be usedto designate like numbers as the embodiments of FIGS. 8-10.

In FIG. 12, valving 36 is illustrated for loading of sample into sampleretainer 58. The sample stream flows in line 70 through ports 36 e and36 d, line 56 sample retainer 58, line 60, ports 36 a and 36 f to waste.To maintain flow through device 8, eluent is pumped from eluentgenerator 32 by pump 30 through ports 36 b and 36 c through column 40 toinlet port 14 a of channel 14, out outlet port 14 b to recycle in line78 to inlet port 12 a through channel 12 and out port 12 b. From there,the stream flows through detector 46, port 10 a, channel 10, and outletport 10 b through inlet port 16 a of channel 16 and outlet port 16 b towaste.

Referring to FIG. 13, the apparatus of FIG. 12 is used for suppressedion chromatography in which sample is injected into column 40. Here, thesample stream flowing in line 70 flows through ports 36 e and 36 f towaste. Eluent from eluent generator 32 is pumped by pump 30 in line 34through ports 36 b and 36 a through line 60, to carry sample in sampleretainer 58 to line 56, and ports 36 d and 36 c to column 40 and fromthere to inlet port 14 a and through channel 14. Solution exitingchannel 14 flows through port 14 b, line 78 through inlet port 12 athrough channel 12 to detector 46. From there, the solution flowsthrough channel 10 and then through channel 16 to waste. During thesample injection mode, a first suppression step is performed in channel14 and a second suppression step is performed in channel 12 prior todetection by detector 46.

Referring to FIG. 11, the ion flow of this double pass embodiment isillustrated. Flow through suppression channels 12 and 14 is concurrent.Thus, suppression begins at the inlet section adjacent port 12 a forchannel 12 and port 14 a for channel 14. The eluent counter ion in thesolution exiting port 14 b is partially suppressed and so is illustratedin salt form although part of the eluent counter-ion has been suppressed(removed). The doubly suppressed sample in acid or base form exits port12 b for flow to detector 46.

By use of the double pass flow system of FIGS. 11-13, the capacity ofthe suppressor device is significantly enhanced because of theadditional residence time in the suppressor device. Also, the wattageper unit area of an eluent screen in a suppressor channel is diminished,leading to lowered waste and improved lifetime of the suppressor device.

FIG. 14 illustrates ion flow of the system of FIGS. 12 and 13 used in asolvent application. Flow through suppression channel 14 is concurrent.Thus, suppression begins at the inlet section adjacent port 14 a forchannel 14 similar to a standard suppressor. The sodium ion which is thecounter ion to the eluent is removed via barrier 22 and is sent towardsthe cathode 26 by the applied potential. Hydronium is transported fromthe anode 24 via barriers 18 and 20 and enters channel 14. The solventin the eluent diffuses towards channel 12 as illustrated by transport ofmethanol represented here as MeOH. The solvent MeOH is diluted by thedeionized water flow in channel 12 and is routed to waste. The flow inchannel 12 is concurrent to the eluent channel flow in channel 14. Ingeneral, this embodiment shows improved compatibility with the solvent.Typical solvents used for ion chromatography can be used in this modesuch as methanol, acetonitrile, isopropyl alcohol and the like. The keybenefit of this mode is that the alcohol is not directly exposed to theanode where oxidation would result in other species that would bedetrimental for chromatography. For example methanol can be oxidized toformate which in the weak formic acid form can permeate the membranes.Since in this mode there is an extra channel 12 between the anode 24 andthe suppressing channel 14 the diffusion of any oxidized species isconsiderably diminished.

The above aqueous liquid stream embodiments have described a dualfunction integrated into four-channel device. However, in methods ofusing such a device, a user has the option to use only one of the twofunctions where an aqueous liquid stream flows through the particularchamber that is not performing its function. For example, an integratedpre-treatment/suppressor device may be used such that only the samplepre-treatment channel is active or that only the suppressor channel isactive. More particularly, the integrated pre-treatment/suppressordevice may have only the pretreatment channel active where anindependent aqueous stream is flowed through the second channel 12(suppressor channel) instead of eluent and separated sample. Similarly,the integrated pre-treatment/suppressor device may have only thesuppressor channel active where an independent aqueous stream is flowedthrough the third channel 14 (sample pretreatment channel) instead ofunseparated sample.

In another example, an integrated suppressor/salt generator device maybe used such that only the suppressor channel is active or that only thesalt generator channel is active. More particularly, the integratedsuppressor/salt generator device may have only the suppressor channelactive where an independent aqueous stream is flowed through the thirdchannel 14 (salt generator channel) instead of a suppressed samplestream. Similarly, the integrated suppressor/salt generator device mayhave only the salt generator channel active where an independent aqueousstream is flowed through the second channel 12 (suppressor channel)instead of eluent and separated sample.

In yet another example, an integrated double suppressor device may beused such that only one suppressor channel is active or that bothsuppressor channels are active. More particularly, the integrated doublesuppressor device may have only one suppressor channel active where anindependent aqueous stream is flowed through the third channel 14(second suppressor channel) instead of a suppressed sample stream. Theoutput from the one suppressor channel can be in fluid communicationwith a detector.

In another aqueous liquid stream embodiment of a four-channel device, aliquid sample stream containing unseparated analytes ion and counterionsto the analyte ions can be pretreated in one of the channels. A detectormay be placed at the outlet of the pretreatment channel to monitor thepurity of the pretreated sample stream. More particularly, the liquidsample stream can be pretreated in the pretreatment channel such as, forexample, the third channel as described in FIGS. 2, 5, and 14. Suitably,an aqueous liquid stream from an independent source may be used as theaqueous liquid stream flowing through one or all of the first, second,and fourth channel.

By isolating the regenerant channel 10 from the solvent in channel 14via use of an additional channel 12 which has deionized water, migrationof the solvent to the anode 24 is minimized. This means any oxidizingreactions at the anode are also minimized. The net effect is thatsolvent compatibility of the suppressor is improved without compromisingsuppression. It should be noted that the independent deionized waterflow in the three channels 10, 12 and 16 is the most preferred format.Depending on the extent of solvent diffusion, the waste from one of thechannels could be the source of the deionized water of the otherchannel.

In order to illustrate the present invention, the following non-limitingexamples of its practice are provided.

EXAMPLE 1 Pretreatment and Suppression

A device as illustrated in FIG. 1 was assembled for the anion analysisand was used to pretreat the sample and suppress the cation counter-ionsin the anion sample prior to injection into the column as illustrated inFIG. 2. The assembly was similar to the Dionex commercial three-channelsuppressor model ASRS 300 (4 mm), except it includes three ion exchangemembranes defining four channels. A five anion standard was used in thisapplication after diluting this tenfold. The five anions in the standardwere fluoride (2.0 ppm), chloride (3.0 ppm), sulfate (15 ppm), nitrate(10 ppm) and phosphate (15 ppm). The standard was delivered to thesample polishing or pretreatment channel by an auto sampler (DionexAS40). Channel 14 a of FIG. 2 was used for the sample pretreatmentaspect. An IonPac® AS18 chromatography column was used for theseparation at a concentration of 32 mM KOH. The flow rate was 1 mL/minand the sample loop had a 25 μL volume. The applied current was therecommended current of 80 mA and complete suppression of the eluent wasachieved with good separation of all peaks. The performance of the unitwith and without sample pretreatment was evaluated to ensure that theunit was capable of pursuing sample pretreatment applications as well asthe suppression applications and the results showed a comparableperformance in peak area as shown in FIGS. 15-16 and Table 1. Note thatpeak 3 in FIGS. 15-16 represents a small impurity of carbonate. Furtherthe results also validated that the chromatographic properties of thepeaks such as peak shape (peak efficiency, asymmetry) are preserved andare not affected by the added new function of the device. These resultsdemonstrate that the suppressor unit of the present invention wouldallow sample pretreatment in conjunction with suppression for criticalapplications.

TABLE 1 Peak Area with sample Peak Name Peak Area Control pretreatment1 - Fluoride 0.9096 0.8701 2 - Chloride 0.7967 0.7714 4 - Sulfate 3.01312.9383 5 - Nitrate 1.4923 1.4630 6 - Phosphate 1.3110 1.2620

EXAMPLE 2 Double Pass

A setup of the device of FIG. 1 was used to test the double-passembodiment for anion analysis of FIG. 11-13. The conditions wereidentical to Example 1. Here the eluent was routed through channel 14for a second time (double pass) and compared with the performance whenthe eluent was only routed through the eluent channel (single pass).Nearly identical performance in peak response was observed for thesingle-pass and double pass embodiments demonstrating the utility ofthis approach as shown in FIGS. 17-18 and Table 2.

TABLE 2 Peak Name Peak Area Single Pass Peak Area Double Pass 1 -Fluoride 0.9096 0.9097 2 - Chloride 0.7967 0.7977 4 - Sulfate 3.01313.0022 5 - Nitrate 1.4923 1.4948 6 - Phosphate 1.311 1.2554

The results indicated that the device of the present invention cansuppress by a double pass approach. Further the results also validatedthat the chromatographic properties of the peaks such as peak shape(peak efficiency, asymmetry) are preserved and are not affected by theadded new function of the device. The double pass approach allowsimproved dynamic capacity for the suppression function. This means ahigher eluent strength can be suppressed by the present inventionwithout compromising significantly on the peak shapes. For high eluentstrength the devices of the prior art would require two or moresuppressors in series. In the present approach by using a single devicethe costs are minimized and higher eluent strength can be suppressed.

EXAMPLE 3 Pretreatment and Suppression

This example illustrates sample pretreatment and suppression in afour-channel device. The device of FIG. 1 was assembled for the CSRSformat (4 mm, cation sample) and was used to suppress the anion counterions to the sample prior to injection into the column. A six cationstandard was used in this application, which contained lithium (0.5ppm), sodium (2.0 ppm), ammonium (2.5 ppm), potassium (5.0 ppm),magnesium (2.5 ppm), and calcium (5.0 ppm). The channel close to theanode was used for the sample pretreatment aspect. An IonPac CS12Acolumn was used for the separation at a concentration of 20 mM MSA. Theflow rate was 1 mL/min and the column temperature was 30° C. The appliedcurrent was the recommended current of 59 mA and complete suppression ofthe eluent was achieved with good separation of all peaks. Theperformance of the unit with and without sample pretreatment showed acomparable performance in peak area as shown in FIGS. 19-20 and Table 3.The performance of the unit with and without sample pretreatment wasevaluated to ensure that the unit was capable of pursuing samplepretreatment applications as well as the suppression applications andthe results showed a comparable performance in peak area. Further theresults also validated that the chromatographic properties of the peakssuch as peak shape (peak efficiency, asymmetry) are preserved and arenot affected by the added new function of the device. These resultsdemonstrate that the suppressor unit of the present invention wouldallow sample pretreatment in conjunction with suppression for selectedapplications.

TABLE 3 Peak Area with sample Peak Name Peak Area Control pretreatment1 - Lithium 0.415 0.423 2 - Sodium 0.525 0.536 3 - Ammonium 0.594 0.64 - Potassium 0.894 0.905 5 - Magnesium 1.272 1.281 6 - Calcium 1.5921.631

EXAMPLE 4 Double Pass

In this experiment, the system of FIG. 1 was assembled for a double passas in FIGS. 11-13 for the CSRS format (cation analytes) and was used tosuppress various concentrations of methanesulfonic acid eluent. Thesuppressor was able to easily suppress 170 mM of MSA at a flow rate of 1mL/min at a set current of 500 mA. The standard suppressor was able tosuppress a maximum capacity of 110 mM of MSA at 1 mL/min at a setcurrent of 330 mA. By using two channels, the suppressor of the presentinvention could suppress a higher concentration of the eluent. It shouldbe noted that the power supply in use had a maximum current of 500 mAhence higher concentrations were not tested.

EXAMPLE 5

A CSRS device of the present invention was tested as per theconfiguration shown in FIG. 1 except only suppression was pursued. Theunit was tested with a cation test matrix for 30 injections. The peakarea RSD's showed an excellent reproducibility of the setup as shown inFIG. 21 and Table 4. These results indicate that the present deviceworks well as a suppressor and shows reproducible performance for thiskey function. In addition the device is capable of pursuing sample prepapplications as shown in the previous examples. The device of thepresent invention can also be used for the suppressor function if neededand this is illustrated in this example.

TABLE 4 Peak Area Reproducibility Performance (% RSD) Peak Name % RSD1 - Lithium 0.168 2 - Sodium 0.128 3 - Ammonium 0.1 4 - Potassium 0.0935 - Magnesium 0.08 6 - Calcium 0.072

EXAMPLE 6

The device of FIG. 1 was used for sample pretreatment and suppression asper the present invention in the system of FIGS. 2-4. In this case, thesample comprised of a five anion standard that was dissolved in a samplecontaining 50 mM sodium hydroxide. The sample comprised a mixture offluoride (Peak 1, 2.0 ppm), chloride (Peak 2, 3.0 ppm), Carbonate (Peak3, Concentration not determined), Sulfate (Peak 4, 15 ppm), Nitrate(Peak 5, 10 ppm) and Phosphate (Peak 6, 15 ppm). A concentrator columnwas used in this application to concentrate a 20 μL injection of thesample anions prior to analysis. An AS15 (4×250 mm) column was used forthe separation and was operated with 38 mM potassium hydroxide eluent at1.2 mL/min. The suppressor of the present invention was operated with acurrent of 113 mA which is the recommended current for the standardthree channel prior art suppressor. A control run was also pursued witha standard suppressor without sample pretreatment using a commercialASRS 300 suppressor of the prior art. Under the conditions of theexperiment without the sample pretreatment step, the commercialsuppressor device showed poor recovery of the anions of interest asexpected especially for the early elutors such as fluoride. In contrastthe device of the present invention could pretreat the sample and removethe interfering matrix ions and therefore achieve good recovery of theanalytes of interest was achieved as illustrated in FIGS. 22 and 23, andTable 5 that show the peak response in peak area counts. The peak areacounts for fluoride for a sample without pretreatment was 0.0467 versus0.5553 for the same peak but with sample pretreatment as per the presentinvention. This demonstrated that the device of the present inventionwas suited for sample pretreatment applications in conjunction withnormal suppression function. Excellent peak shapes were observed withthe device of the present invention.

TABLE 5 With out Sample With Sample Peak # Pretreatment Pretreatment 1 -Fluoride 0.0467 0.5553 2 - Chloride 0.1646 0.6218 3 - Carbonate 0.6842.0912 4 - Sulfate 1.0254 2.4645 5 - Nitrate 0.4336 1.1307 6 - Phosphate0.5456 0.9896

EXAMPLE 7

The setup of the device of Example 2 was used in this experiment exceptthe column was bypassed with a restrictor tubing that generated apressure of about 1000 psi and the maximum suppression capacity of thedevice was studied by pumping in an eluent comprising of 200 mM sodiumhydroxide. The double pass experiment was repeated with an appliedcurrent of 500 mA. The maximum suppression capacity was studied bymonitoring the conductivity signal post suppression and by incrementallychanging the flow rate from 1.0 mL/min by increments of 0.05 mL/min. Ifcomplete suppression was observed the background was low. Under theseconditions the device of the present invention was able to suppress upto about 290 μeqv/min with an applied current of 500 mA. The aboveexperiment was also repeated with a standard ASRS 300 suppressor whichshowed a suppression capacity of about 210 μeqv/min, which issignificantly lower than the double pass approach. The abovedemonstrates the utility of the device of the present invention tosuppress a higher concentration of eluent.

What is claimed is:
 1. A liquid chromatography system comprising: (a) anelectrolytic device configured to suppress an eluent or pretreat aliquid sample, the electrolytic device comprising: (i) a housingincluding first, second, third, and fourth side-by-side liquidflow-through channels, each having an inlet and an outlet; (ii) thefirst channel being separated from the second channel by a first chargedbarrier having exchangeable ions capable of passing ions of only onecharge, positive or negative, and of blocking bulk liquid flow; (iii)the second channel being separated from the third channel by a secondcharged barrier having exchangeable ions capable of passing ions of thesame charge, positive or negative, and of blocking bulk liquid flow;(iv) the third channel being separated from the fourth channel by athird charged barrier having exchangeable ions capable of passing ionsof the same charge, positive or negative, and of blocking bulk liquidflow, wherein the first charged barrier, the second charged barrier, andthe third charged barrier all have a same charge; (v) a first electrodedisposed adjacent to and along the first channel in electricalcommunication therewith; and (vi) a second electrode disposed adjacentto and along the fourth channel in electrical communication therewith,the liquid chromatography system further comprising: (b) achromatographic separator having an inlet and an outlet, thechromatographic separator outlet being upstream of and in fluidcommunication with the second channel inlet; and (c) a first detector,the second channel outlet being upstream of and in fluid communicationwith the first detector.
 2. The liquid chromatography system of claim 1further comprising: valving and a concentrator or a sample loop; thevalving having a first position configured to load the liquid sampleinto the concentrator or the sample loop and to block the flow of theliquid sample to the chromatographic separator inlet and a secondposition configured to establish fluid communication with theconcentrator or the sample loop and the chromatographic separator inlet.3. The liquid chromatography system of claim 1, in which the firstdetector is in fluid communication with the first channel inlet.
 4. Theliquid chromatography system of claim 1, in which the second channelinlet and the third channel inlet are disposed at opposite ends of theirrespective channels so that liquid flow through the second channel andthe third channel is countercurrent.
 5. The liquid chromatography systemof claim 1, in which the second channel inlet and the third channelinlet are disposed at a same end of their respective channels so thatliquid flow in the second channel and the third channel is concurrent.6. The liquid chromatography system of claim 2, in which the firstdetector also is in fluid communication with the third channel inlet. 7.The liquid chromatography system of claim 1, in which the third channeloutlet is in fluid communication with a second detector.
 8. A liquidchromatography system comprising: (a) an electrolytic device configuredto suppress an eluent, the electrolytic device comprising: (i) a housingincluding first, second, third, and fourth side-by-side liquidflow-through channels, each having an inlet and an outlet; (ii) thefirst channel being separated from the second channel by a first chargedbarrier having exchangeable ions capable of passing ions of only onecharge, positive or negative, and of blocking bulk liquid flow; (iii)the second channel being separated from the third channel by a secondcharged barrier having exchangeable ions capable of passing ions of thesame charge, positive or negative, and of blocking bulk liquid flow;(iv) the third channel being separated from the fourth channel by athird charged barrier having exchangeable ions capable of passing ionsof the same charge, positive or negative, and of blocking bulk liquidflow, wherein the first charged barrier, the second charged barrier, andthe third charged barrier all have a same charge; (v) a first electrodedisposed adjacent to and along the first channel in electricalcommunication therewith; and (vi) a second electrode disposed adjacentto and along the fourth channel in electrical communication therewith,the liquid chromatography system further comprising: (b) achromatographic separator having an inlet and an outlet, thechromatographic separator outlet being upstream of and in fluidcommunication with the third channel inlet, the third channel outletbeing upstream of and in fluid communication with the second channelinlet; and (c) a first detector, the second channel outlet beingupstream of and in fluid communication with the detector.
 9. The liquidchromatography system of claim 8, in which the detector is also in fluidcommunication with the first channel inlet.
 10. A method for pretreatinga liquid sample containing analyte ions of one charge, positive ornegative, and counterions to the analyte ions and for suppressing aneluent containing the analyte ions, in an electrolytic devicecomprising: (a) a housing including first, second, third, and fourthside-by-side liquid flow-through channels, each having an inlet and anoutlet; (b) the first channel being separated from the second channel bya first charged barrier having exchangeable ions capable of passing ionsof only one charge, positive or negative, and of blocking bulk liquidflow; (c) the second channel being separated from the third channel by asecond charged barrier having exchangeable ions capable of passing ionsof the same charge, positive or negative, and of blocking bulk liquidflow; (d) the third channel being separated from the fourth channel by athird charged barrier having exchangeable ions capable of passing ionsof the same charge, positive or negative, and of blocking bulk liquidflow, wherein the first charged barrier, the second charged barrier, andthe third charged barrier all have a same charge; (e) a first electrodedisposed adjacent to and along the first channel in electricalcommunication therewith; and (f) a second electrode disposed adjacent toand along the fourth channel in electrical communication therewith; themethod comprising flowing the liquid sample into the third channel inletthrough the third channel and out the third channel outlet; flowing theeluent into a chromatographic separator to separate the analyte ions;flowing the eluent containing the separated analyte ions into the secondchannel inlet through the second channel and out the second channeloutlet; applying an electric current between the first and the secondelectrodes across the first, the second, the third, and the fourthchannels to cause ions of opposite charge to the separated analytes toflow toward one of the two electrodes to remove at least some of thecounterions in the liquid sample in the third channel and simultaneouslysuppressing the eluent flowing in the second channel.
 11. The method ofclaim 10 further comprising: flowing the eluent from the second channeloutlet to a first detector for detecting the separated analyte ions. 12.The method of claim 10 further comprising: concentrating the analyteions from the third channel on a sample retainer; and flowing theconcentrated analyte ions from the sample retainer with the eluent andthen to the chromatographic separator.
 13. The method of claim 10further comprising: loading the liquid sample from the third channel ina sample loop; flowing the loaded liquid sample with the eluent and thento the chromatographic separator.
 14. The method of claim 10, in which aflow of the eluent through the second channel is concurrent to a flow ofthe liquid sample through the third channel.
 15. The method of claim 10,in which a flow of the eluent through the second channel iscountercurrent to a flow of the liquid sample through the third channel.16. The method of claim 12 further comprising: flowing the eluent fromthe first detector to the first channel inlet and through the firstchannel.